The present invention relates to the general field of combustion chambers for turbomachines. More particularly, it relates to the problem posed by fastening an annular combustion chamber for a turbomachine to the casing of the turbomachine.
Conventionally, the annular combustion chamber of a turbomachine is made up of inner and outer annular walls interconnected by a transverse wall forming the end of the chamber. The end of the chamber is provided with a plurality of openings having fuel injectors mounted therein.
At their downstream ends, the inner and outer walls of the combustion chamber are generally extended by likewise annular inner and outer flanges that are designed to be fastened respectively to the inner and outer shells of the turbomachine casing. These flanges serve to hold the combustion chamber in position inside the turbomachine casing.
Air coming from a compressor stage of the turbomachine located upstream from the combustion chamber flows between the shells of the casing and the annular walls of the chamber. This air which penetrates into the chamber in particular via holes formed through the walls of the chamber participate in the combustion of the air/fuel mixture.
Furthermore, a fraction of this air serves to feed a circuit for cooling the high pressure turbine of the turbomachine that is disposed downstream from the combustion chamber.
For this purpose, the inner fastening flange of the combustion chamber is typically pierced by a plurality of holes that allow air to pass from the compressor to a cooling circuit of the high pressure turbine. These holes are generally uniformly spaced apart along a row over the entire circumference of the inner flange.
The inner shell of the casing of the turbomachine is also pierced by a plurality of orifices that open out into the annular space defined between the inner shell and the inner flange for fastening the chamber, and that also open out towards the cooling circuit of the high pressure turbine.
Drilling air feed holes through the inner flange for fastening the combustion chamber raises problems of its ability to withstand the vibration generated by combustion of the air/fuel mixture in the chamber.
The combustion frequencies of the air/fuel mixture in the chamber cause vibration in the chamber walls which propagates to the fastener flanges. The fastener flanges must therefore be sufficiently flexible to damp such vibration, but also sufficiently rigid to perform their function of holding the combustion chamber in position in the casing.
Unfortunately, the presence of holes through the inner fastener flange weakens the ability of the flange to withstand vibration. Vibration in the walls of the chamber, associated with a regular distribution of the holes in the inner flange, leads to a vibratory resonance phenomenon that leads to a risk of the inner flange breaking, in particular between two adjacent holes.